Blow molding process for container of superplastic alloy

ABSTRACT

A container of a superplastic alloy material is manufactured by causing a fluid to blow into a bottomed cylinder. Prior to the blow molding, the cylinder has its surfaces finished smooth and is preheated in a temperature range of 200* - 300*C at least two minutes. Within a metal mold, the cylinder is subjected to an initial pressure of at least 8 atm., and is thereafter subjected to a molding pressure in the range of 7 - 20 atm. into the container blown out to the final dimensions. Since the molding pressure is lastly bestowed after somewhat inflating the cylinder by the initial pressure, the product is blowmolded finely, and a beautiful container having neither a flaw nor a crack on the surface is obtained.

Umted States Patent 1191 1111 3,896,648 Schertenleib July 29, 1975 [54]BLOW MOLDING PROCESS FOR 3,529,458 9/1970 Butler et a1. 72/60 CONTAINER0F SUPERPLASTIC ALLOY 3,535,766 10/1970 Hymes 29/42l [75] inventor:Francis Schertenleib, Furstentum, Primary Examiner Richard J. HerbstLlechtenstem Attorney, Agent, or Firm-Stevens, Davis, Miller & [73]Assignee: Alter Licensing Establishment, Moshe" Vaduz, Liechtenstein 221Filed: May 31, 1974 [571 f ABSTRACT I A container 0 a superplastic alloymaterial is manu- [211 Appl' 474964 factured by causing a fluid to blowinto a bottomed cylinder. Prior to the blow molding, the cylinder has[30] Foreign Application Priority Data its surfaces finished smooth andi8 preheated in temo 2, 1973 J 48-110915 Peratue range 300C at least twoct apan Within a metal mold, the cylinder is subjected to an 52 US. 01.72/61; 72/364' 29/421 initial Pressure Ofat least 8 and is thereafter 51Int. Cl B2l d 26/04 J'ected a "mlding Pressure in the range of 7 20 [58]Field of S 72/56 57 58 59 60, atm. into the container blown out to thefinal dimen- 72/6l 62 364 i l sions. Since the molding pressure islastly bestowed Q5/3875: after somewhat inflating the cylinder by theinitial pressure, the product is blowmolded finely, and a [56]References Cited beautiful container having neither a flaw nor a crackUNITED STATES PATENTS on the surface is obtained.

3,340,101 9/1967 Fields Jr. et al. 148/] 1.5 6 Claims, 10 DrawingFigures -IrllIIIIIIIII The present invention relates to a containermanufactured of an alloy of superplasticity, and more particularly to amethod of manufacturing a container by blowing a tube of a superplasticalloy.

Since the superplastic alloy spreads extraordinarily largely by a lowworking stress, it is subjected to such molding working as rolling.drawing, sheet working, press forging and extrusion. Further, thedevelopment of a manufacturing technique based on the blow molding isattempted recently. Unlike glass or plastics, however, the superplasticalloy is narrow in the temperature region in which it exhibits thesuperplastic flow, and does not always respond to a sudden workingstress. It is therefore limited in moldability. ln consequence, evenwhen the superplastic alloy is extraordinarily expanded compulsorily bymerely raising the blow pressure, it cannot be uniformly molded.Particularly the molding of elaborate parts becomes imperfect, and anon-uniform thickness of the molded article or cracks in the surfacearise. In this manner, the manufacture with the superplastic alloy hasbeen technically unsolved.

The present invention intends to produce a novel container by utilizingthe property of the superplastic alloy. Since the conventionaltechniques have worked the superplastic alloy under a conditionexceeding the limit of thee moldability thereof, they have beenincapable of manufacturing a product enduring practical use. Theinvention has therefore accomplished the intention by the blow formationof the container in such way that a material is preheated so as tomanifest the superplastic phenomenon, that it is somewhat inflated by alow initial pressure of at least 8 atm., and that it is thereafter givena molding pressure in the range of 7 atm. Previously to the preheatingof the superplastic alloy, the material is formed into a bottomedcylinder, the surfaces are smoothed and the dimensional precisions arearranged. Thus, the external appearance of the product by the blowmolding is made beautiful, and the outward dimensions of the finishedarticle are made accurate.

Used the superplastic alloy are Zn Al (78 22), Al Cu (67 33), Al Si(88.3 11.7), Mg A1 (67.7 32.3), Mg Cu (69.3 30.7), Mg Ni (76.5 23.5),and so forth. These alloys are preheated at 200 300C at least 2 minutes,and while kept at a molding temperature below 600C, they are molded bythe blow formation at a blow ratio of at the greatest 3 under the twostages of molding pressures.

In accordance with the present invention, there are two cases. one ofwhich starts from the stage of work of making a bottomed cylinder from aslab or discshaped member of the superplastic alloy material, while theother starts from the stage of work of making a bottomed cylinder byclosing the bottom ofa pipe obtained by the extrusion molding. In eithercase, a container of desired size and shape can be readily manufacturedby placing the bottomed cylinder in a metal mold and subjecting it tothe blow formation under the conditions as mentioned above.

As apparent from the foregoing, the principal object of this inventionis to provide a method which can manufacture a container of asuperplastic alloy material.

Another object of this invention is to provide a method which canmanufacture a container by the technique of blowforming a superplasticalloy material.

Still another object of this invention is to provide a container whichis made of a superplastic alloy material.

The above-mentioned and further objects of the present invention willbecome more definite from the following detailed description when readwith reference to the accompanying drawings. In the drawings, likereference symbols indicate like constituent parts.

FIG. 1 is a perspective view ofa slab ofa superplastic alloy material.

FIG. 2 is a sectional view of a bottomed cylinder which is obtained bythe impact molding. the compression molding or the vacuum molding of theslab;

FIG. 3 is a sectional view illustrating the state under which thecylinder is ironing-worked;

FIG. 4 is a sectional view illustrating the state under which the insidesurface of the cylinder at its opening is machined;

FIG. 5 is a sectional view illustrating the state under which the insidesurface of an inner part of the cylinder as is distant from the openingpart is machined;

FIG. 6 is a sectional view illustrating the state under which thecylinder is inserted into a metal mold assembly in the open state;

FIG. 7 is a sectional view illustrating the state under which the metalmold assembly in FIG. 6 is closed and under which the cylinder is blownout;

FIG. 8 is a front view of a finished product (container);

FIG. 9 is a perspective view ofa tube ofa superplastic material; and

FIG. 10 is a sectional view of the tube in FIG. 9 as is made a bottomedcylinder.

As previously stated, the present invention has the case of startingfrom the slab of a superplastic alloy and the case of starting from thetube thereof. In either case, it includes the various steps ofpreparation of the bottomed cylinder, mechanical preprocessing,preheating, blow formation, cooling, taking out the molded article, andfinishing.

(Embodiment) 7 Description will now be made of the first case.

lst Step: A slab l as shown in FIG. 1 is made in such way that a rolledmaterial of superplastic alloy (Zn 78 Al 22 percent) having a suitablethickness as required for manufacturing a final product, for example, acontainer 10 shown in FIG. 8 is punched into a predetermined size andshape. Alternatively, the slab is made by slicing an extruded bar ofpredetermined sectional shape at a fixed thickness.

2nd Step: A bottomed cylinder 2 as shown in FIG. 2 is made by subjectingthe slab 1 to the impact molding, the compression molding or the vacuummolding. In the middle of the bottom 12 of the cylinder 2, a lug 15 isformed. Up to this step, the molding must be executed within the regionof the superplastic property of the alloy. The temperature, the heatingperiod of time, etc. need be sufficiently considered.

3rd Step: For the external appearance, thickness distribution, moldingetc. of the final product (container) 10, the surfaces of the cylinderare subjected to a preprocessing such as polishing, ironing working(drawing working) and machining. The expression polishing" signifiesthat with a file and/or buff, and it serves to increase the luster andsmoothness of the outside surface of the cylinder. The ironing workingdraws or squeezes the cylinder 2 with a die 3 as illustrated in FIG. 3.Thus, the material of the cylinder surface 2,, is stretched, to enhancethe smoothness of the surface, to remove cavities created in the outsidesurface and to render the structure of the material finer. so as toobtain a container whose outside surface is beautiful. The machiningsignifies to cut and work the inside surface 2,, of the cylinder inconformity with the shape of the final container as illustrated in FIG.5. Thus. the thickness distribution is made uniform. In order to relievea small protuberance, for example. a screw portion 11 to be formed onthe outer periphery of the neck portion of the final container 10 asshown in FIG. 8, the inside surface 2,- of the corresponding part of thecylinder is cut and worked thin as illustrated in FIG. 4. Thus, the neckportion is inflated well at the stage of work of blowing-out.

4th Step: Before the cylinder having undergone the first to third stepsis shifted to the blow step, it is subjected at this fourth step topreheating at 260C i lC for about 10 to 15 minutes. In this case, whenthe temperature of 270C is exceeded, the thermoplasticity decreases.When the cylinder is held at 300C for a certain period of time (forexample, 15 minutes), the thermoplastic property is conspicuously lost,and the blowing-out becomes impossible. However, when the alloy isquenched at 350C again, the superplastic property is restored. A furnacestructure for executing the preheating shall be one which changes littlein the temper ature difference at the opening and closure. It is furthernecessary to make control so that an abrupt temperature fall may beprevented when the preheated cylinder is transferred to a blow moldassembly.

5th Step: The fifth step is the blow step. The preheated cylinder 2 isshifted to the blow step, which is generally performed in the order ofthe following substeps (I (5)- l. The right and left split molds of themetal mold assembly are closed.

2. The bottom mold of the metal mold assembly is pushed up and set, toconstruct the blow mold assembl 5. The preheated cylinder is insertedand arranged in the blow mold assembly.

4. The cylinder is heated. It is held at 260C i C by heaters inside themetal mold assembly.

5. A nozzle is inserted into the heated cylinder, and air or a gas iscaused to blow thereinto. The cylinder is blown out until it becomes theshape of the final container.

FIG. 6 illustrates the state under which the metal mold assembly isopen. The metal mold assembly consists of the right and left split molds4, 4 and the bottom mold 6. Each of the split molds 4, 4 contains theheater 7 therein. A cavity 8 for molding the final product 10 is formedinside each split mold, while a neck portion 9 for molding the portportion of the final product is formed at the upper edge. When the metalmold assembly is open, the cylinder 2 is inserted into a position shownin FIG. 6. Subsequently, the split molds 4, 4 are registered, and thebottom mold 6 is raised. At this time, the lug located in the middle ofthe bottom 12 of the cylinder 2 is inserted into a depression 16 in themiddle of the bottom mold 6. Subsequently, as illustrated in FIG. 7, themetal mold assembly is closed, and

the cylinder is inflated by causing the fluid to blow thereinto from theblast port 14 of the nozzle portion 13. Since the cylinder has itscentral position held with the lug 15 of the bottom portion insertedinto the depression 16 of the bottom mold 6, it is inflated at equalrates in the radial direction, and any partial thickness is prevented.As a modification, it is also allowed to provide the lug in the middleof the bottom mold 6 and to form the depression at the bottom of thecylinder.

The conditions of the blow molding at the sub-step (5) are as follows.

The blow time is 45 to 60 seconds. the initial pressure is 10 atm. (2 to3 seconds), and the molding pressure is 17 atm. (43 to 57 seconds). Asthe pressure-applying medium, an inert gas, such as nitrogen and argon.heated to C C is used in order to prevent the molding compact from beingoxidized and lowering in temperature. The molding pressure is not oncegiven at the molding, but an appropriate ratio for the elongation of thematerial is promoted by the initial pressure so that the cylinder can bemolded into the precise shape of the final container. When the cylinderis blown out directly by the molding pressure without going through theinitial pressure, a weak part dependent upon the thickness distributionis suddenly inflated to give rise to a thickness change and a shapechange. This drawback is eliminated by the initial pressure. The maximumblow ratio at this time was 2.7 in experiments.

6th Step: After the molding. cooling with air is carried out in order tofacilitate the release of the molding compact from the metal moldassembly. The cooling time is 5 to 6 seconds.

7th Step: This is a mold opening and product takingout step. Theblown-out container of the final shape is taken out from the metal moldassembly manually or automatically.

8th Step: This is a finishing step. The molded container is subjected tothe various finishing sub-steps of l slicing and cutting the portportion. (2) washing the inside and outside of the container, (3)plating the outer surface of the container or coating it with paint. and(4) coating the inner surface of the container. (Modified Method)Description will now be made of the second case, namely. the methodwhich starts from making a bottomed cylinder by providing a bottom foran extrusionmolded tube.

lst Step: By the extrusion molding, a tubular body 20 is molded as shownin FIG. 9.

2nd Step: A bottom portion 22 is formed by blocking one end of the tube20, so that a cylindrical body 21 as shown in FIG. 10 is prepared. Inthe middle of the bottom 22, a lug 23 is provided. In this case, thereis employed either a method (A) in which the bottom portion is formed byheating and welding a separate component of the same alloy as that ofthe cylinder, or a method (B) in which the bottom portion is formed bynipping one end of the cylinder by means of a metal mold or any othermechanism.

The third and succeeding steps are the same as in the first case.However, since the thickness change of the cylinder is achieved at theextrusion molding, the ironing working and the machining as seen at thethird step of the first case are omitted.

As described above, the present invention can readily mold a metalliccontainer in such way that, after finishing the inside and outsidesurfaces of a cylinder of a superplastic alloy material, the steppedblow molding from the initial pressure to the molding pressure iscarried out. With the conventional compression and impact workings, themolding of the container of the superplastic alloy material is attendedwith difficulties. In contrast. according to the present invention, abeautiful final container can be smoothly molded without losing thesmoothness of the surfaces and without causing partiality in thicknessand cracks, in such way that the blow pressure is bestowed stepwisewhile maintaining the temperature of the process in which the internalstructure of the material changes.

The container produced by the present invention can be extensively usedlikewise to metallic containers which are usually employed for receivingdrinks, cosmetics, liquid medicines, etc.

What is claimed is:

l. A method of manufacturing a blow-molded article of a container madeof a superplastic alloy, comprising the steps of:

a. forming a bottomed cylinder from a starting material of saidsuperplastic alloy,

b. performing a mechanical finish processing for smoothing the surfacesof said cylinder and for enhancing the dimensional accuracy,

c. preheating the finish-processed cylinder by holding it in atemperature range of 200 to 300C for at least two minutes,

d. receiving the heated cylinder in a metal mold assembly, and blowingout said cylinder from the port side towards the interior thereof byfluid pressures of an initial pressure of at least 8 atm. and a mold-LII ing pressure in the range of 7 20 atm., and

e. cooling said metal mold assembly by air blast before it is opened totake out the inflated product therefrom.

2. The method according to claim 1, wherein the superplastic alloymaterial is a member selected from the group consisting of Zn Al, Al Cu,Al Si, Mg Al, Mg Cu and Mg Ni.

3. The method according to claim 1, wherein a lug is formed at thebottom of said bottomed cylinder, while a depression corresponding tosaid lug is formed in a bottom mold of said metal mold assembly, andwhen said metal mold assembly is closed. said lug is inserted into saiddepression so as to hold the central position of said cylinder.

4. The method according to claim 1, wherein the superplastic alloymaterial is subjected to the preheating treatment at 260C 10C for 10minutes to [5 minutes, it is subsequently held under the initialpressure of 10 atm. for 2 to 3 seconds in said metal mold assemblyheated to at most 600C, and it is thereafter blown therein under themolding pressure of 17 atm. for 43 to 57 seconds, so that it is made theinflated container having a maximum blow ratio of 3.

5. The method according to claim 1, wherein said bottomed cylinder isobtained by subjecting a slab of the superplastic alloy material to anyof impact molding, compression molding and vacuum molding.

6. The method according to claim 1, wherein said bottomed cylinder isobtained by providing a bottom at one end of an extrusion-molded tube.

1. A method of manufacturing a blow-molded article of a container madeof a superplastic alloy, comprising the steps of: a. forming a bottomedcylinder from a starting material of said superplastic alloy, b.performing a mechanical finish processing for smoothing the surfaces ofsaid cylinder and for enhancing the dimensional accuracy, c. preheatingthe finish-processed cylinder by holding it in a temperature range of200* to 300*C for at least two minutes, d. receiving the heated cylinderin a metal mold assembly, and blowing out said cylinder from the portside towards the interior thereof by fluid pressures of an initialpressure of at least 8 atm. and a molding pressure in the range of 7 -20 atm., and e. cooling said metal mold assembly by air blast before itis opened to take out the inflated product therefrom.
 2. The methodaccording to claim 1, wherein the superplastic alloy material is amember selected from the group consisting of Zn - Al, Al - Cu, Al - Si,Mg - Al, Mg - Cu and Mg - Ni.
 3. The method according to claim 1,wherein a lug is formed at the bottom of said bottomed cylinder, while adepression corresponding to said lug is formed in a bottom mold of saidmetal mold assembly, and when said metal mold assembly is closed, saidlug is inserted into said depression so as to hold the central positionof said cylinder.
 4. The method according to claim 1, wherein thesuperplastic alloy material is subjected to the preheating treatment at260*C + or - 10*C for 10 minutes to 15 minutes, it is subsequently heldunder the initial pressure of 10 atm. for 2 to 3 seconds in said metalmold assembly heated to at most 600*C, and it is thereafter blowntherein under the molding pressure of 17 atm. for 43 to 57 seconds, sothat it is made the inflated container having a maximum blow ratio of 3.5. The method according to claim 1, wherein said bottomed cylinder isobtained by subjecting a slab of the superplastic alloy material to anyof impact molding, compression molding and vacuum molding.
 6. The methodaccording to claim 1, wherein said bottomed cylinder is obtained byproviding a bottom at one end of an extrusion-molded tube.